Several methods are known in the prior art for converting .alpha.,.beta.-olefinically unsaturated carbonylic compounds into the corresponding .alpha.,.beta.-olefinically unsaturated alcohols.
British Pat. No. 734,247 and U.S. Pat. No. 2,763,696 disclose a process whereby acrolein may be converted to allyl alcohol by means of a vapor phase hydrogenation process. According to this process, moderate yields of allyl alcohol are obtained when acrolein is treated with free hydrogen in the vapor phase at a temperature between 210.degree. and 240.degree. C in the presence of a catalyst comprising cadmium and one or more heavy metals of groups I, II, VI and VIII of the periodic table. Relatively high pressures are employed in the process on the order of 20 to 50 kilograms per square centimeter.
German Pat. No. 858,247 discloses a somewhat different process which is also useful for the conversion of acrolein to allyl alcohol. According to the German patent, good yields of allyl alcohol are obtained by reacting acrolein with free hydrogen in the presence of a catalyst containing cadmium oxide and a metal hydrogenating component which is preferably copper. The patent teaches that the best results are obtained when the process is operated at high temperatures and at high pressures on the order of 100-300 atmospheres.
It is also known to convert .alpha.,.beta.-unsaturated aldehydes into the corresponding unsaturated alcohols in the liquid phase by means of hydrogenation in the presence of a mixture of a copper soap and a cadmium soap. It is assumed that the copper salt is the catalyst and that the cadmium salt only serves the function of preventing the copper salt from being reduced to metallic copper. The use of a solution of a mixture of a copper salt and a cadmium salt for catalyst has the disadvantage that the system is extremely unstable under the required processing conditions, and fluctuations in conditions can cause reduction of the Cd.sup.2+ salt and/or the Cu.sup.2+ salt to metals.
U.S. Pat. No. 3,686,333 describes a liquid phase hydrogenation process for converting alkenals into alkenols in the presence of a catalyst mixture of a cadmium salt of a fatty acid and a transition metal salt of a fatty acid.
Japanese Patent No. 73-01,361 discloses a process for hydrogenating .alpha.,.beta.-olefinically unsaturated aldehydes into the corresponding allylic alcohol derivatives. The efficiency of the process is improved by the recycle of by-products to the hydrogenation zone, or by passage of the by-products stream into a second hydrogenation zone. The preferred catalysts are mixtures of cadmium and copper, cadmium and silver, cadmium and zinc, cadmium and chromium, copper and chromium, and the like. The Japanese patent states that under steady state conditions 1.5 moles/hour of acrolein are converted to 1.05 moles/hour of allyl alcohol and 0.4 mole/hour of n-propanol.
There remains a need for a commercially feasible vapor phase process for converting .alpha.,.beta.-olefinically unsaturated carbonylic compounds into allylic derivatives in higher efficiency and yield then has been achieved heretofore in the prior art.
Accordingly, it is an object of the present invention to provide an improved process for producing allylic alcohol derivatives by hydrogenation of .alpha.,.beta.-olefinically unsaturated carbonylic compounds.
It is another object of the present invention to provide a process for converting acrolein into allyl alcohol with a conversion of at least 95 percent and a yield of at least 70 percent.
It is further object of the present invention to provide a novel silver-cadmium alloy catalyst for selective hydrogenation of .alpha.,.beta.-olefinically unsaturated carbonylic compound to the corresponding allylic alcohol derivatives.
Other objects and advantages of the present invention shall become apparent from the following description and examples.